1. Field of the Invention
This invention relates to a composite material, particularly a composite material having a novel construction (composition) capable of exhibiting composite functions useful in various industrial fields, and to a method for producing the same.
2. Related Background Art
In the prior art, molded products constituted of a single material can exhibit only the performances inherent in the material employed, and therefore, in order to impart another additional function to those molded products, composite materials combined with other components have been widely used. Typical examples may include composite organic materials such as various colored plastic moldings, various electroconductive plastic moldings, various filler-compounded plastic moldings, etc., composite organic materials such as various special glasses, various ceramics, various alloy materials, various catalysts, etc., and their kinds may be said to be innumerable. Such various kinds of composite materials of the prior art are applied with various contrivances so that the components constituting the composite materials may be uniformly compounded with each other. In the case of forming both components in layers, the molded products formed from the respective materials have been subjected to such means as lamination, fusion, adhesion, etc., to accomplish composite formation.
Various kinds of composite materials of the prior art as mentioned above may be roughly classified into uniform composite materials in which the constituents exist uniformly with each other (e.g. molded product containing electroconductive particles uniformly dispersed in a plastic base) and laminated products in which the constituents are bonded in layers (e.g. vapor-deposited molded product having a metal vapor-deposited thereon). In addition to these composite materials known in the art, it has been also widely desired in various industrial fields to have, for example, a composite material in which its magnetic intensity is varied in at least one direction of the molded product in specific magnetic materials, a composite material in which its electroconductivity is varied in at least one direction of the molded product in electroconductive materials, a composite material in which thermal conductivity is varied in at least one direction in thermal conductive materials, a composite material in which photoconductivity is varied in photoconductive materials, or a material in which these properties are further combined.
In this connection, as the typical method for producing composite optical materials having refractive index distribution, the following methods (1), and (2) have been known in the art.
(1) The so-called ion exchange method in which ions in glass are exchanged with other ions; and
(2) The gas phase synthetic method.
The above ion exchange method involves the essential restriction that ion exchange shall be carried out under the temperature condition at which the glass itself will not be deformed. More specifically, for carrying out ion exchange within practical time, only monovalent cations such as Tl.sup.+, Cs.sup.+, Rb.sup.+, etc., with rapid diffusion speed can be used as the diffusing species. Particularly, when a large refractive index distribution is desired to be obtained, Tl.sup.+ ions are required to be used. However, in this case, it cannot be avoided that the dependency of refractive index on wavelength becomes greater. Also, even when a monovalent cation with greater diffusion speed as mentioned above is used, if a thick rod lens with a diameter of 20 mm or longer is to be prepared by the method applying ion exchange, the required time becomes so long that it cannot be industrially practiced.
On the other hand, as the gas phase synthetic method, VAD (Vapour-Axis Deposition) method and CVD (Chemical Vapour Deposition) method have been known. However, these methods are low in productivity and no large optical element can be obtained with ease.
As described above, under the present state of the art, there is no method for easily producing a high quality composite material having desired composite functions, and there has been known substantially no composite material of high performance which is practical in industry and of low price.